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Tuesday, February 19, 2013

The X-ART tweeter of ADAM Audio loudspeakers (It ISN'T a ribbon!)

OXSA Labs | February 15, 2013

Q:
When is a ribbon tweeter not a ribbon tweeter? A: When it's an eXtended
Accelerating Ribbon Technology tweeter in an ADAM Audio loudspeaker.

ADAM
Audio has set a problem for itself by describing its tweeter as a kind
of ribbon tweeter. It seems, judging from Internet comments, that many
people think it is a ribbon tweeter. But it isn't, quite.

What is normally regarded as a ribbon tweeter has a flat metallic
diaphragm suspended in a magnetic field. Its advantage over the more
usual dome tweeter is that the ribbon works as both radiating diaphragm
and coil, with every part of the ribbon being driven directly. It can
have a frequency response up to 100 kHz that only your pet bat can hear.

Adam Audio's tweeter, although it has the word 'ribbon' in its name,
is more properly called an 'air motion transformer', as invented several
decades ago by Dr. Oskar Heil.

The essential difference between this and a conventional drive unit
is that the diaphragm of a conventional driver moves as fast as the air
in front is required to move to create the desired acoustic wave. The
air motion transformer can however move air four times faster than the
speed of the diaphragm.

Adam Audio has incorporated this technology into its X-ART tweeters.
The diaphragm is folded into a concertina shape that is squeezed by the
incoming audio signal. Compression and expansion of the folds of the
concertina force the air in and out much faster than the motion of the
diaphragm itself.

The advantages of this are, according to ADAM Audio, that the tweeter
has "unprecedented clarity and pristine transient reproduction" and
also "avoids the typical breakup/distortion and subsequent dynamic
limiting at higher frequencies of stiffer voice coil designs". A further
bonus is that the X-ART's equivalent of a coil is in direct contact
with the air and thus can be cooled more efficiently.

Also, by folding the diaphragm, it can cover a much larger area while
remaining compact in terms of its aperture to the air. A smaller
diaphragm aperture has a larger angle of dispersion, which is a
desirable feature for a tweeter in many applications.

Whether this technology can be shown to be subjectively better than a
conventional tweeter will be down to its ultimate acceptance in the
pro-audio marketplace. Or not. It is however a fascinating development
and, as always, we applaud technical progress.